In recent years, a material for a computer to plate system (CTP), in which image data can be directly recorded in a planographic printing plate material without employing an original, has been sought accompanied with the digitization of printing data.
In recent years, a material for a computer to plate system (CTP), in which image data can be directly recorded in a planographic printing plate material without employing an original, has been sought accompanied with the digitization of printing data. Further, a processless CTP system is widely spreading which is capable of being developed only by exposure (on-press development is included), and does not require development by an alkali developer nor an automatic developing machine, in view of space saving and environmental requirement.
In a plate making of a processless CTP, a planographic printing plate material is imagewise exposed, mounted on a plate cylinder of a printing press, and developed with printing ink alone or with printing ink and a dampening solution where unnecessary portions of the exposed planographic printing plate material are removed.
There are, for example, a processless CTP comprising an image formation layer containing heat fusible particles and a water-soluble binder in which the image formation layer at unexposed portions are removed with printing ink and/or a dampening solution (see JP 2938839, and Japanese Patent O.P.I. Publication Nos. 9-123387, 2001-96710, 2001-334766, 2002-361996, 2002-178665, and 2001-33476), and a processless CTP in which the outermost layer is broken by ablation, and the broken portions are removed to reveal a layer different in ink affinity from the outermost layer (see Japanese Patent O.P.I. Publication Nos. 7-164773). These processless CTP has advantages in that plate making is carried out in a short time. However, recently, further shorter plate making time is required, since many kinds of prints in a small number are demanded.
As a method of shortening on-development time (development on a plate cylinder) has been disclosed in Japanese Patent O.P.I. Publication Nos. 2000-52634, 9-123387, and 9-123388, in which when developing the processless CTP on a plate cylinder, optimum timing of supply of a dampening solution and printing ink to the CTP is disclosed. However, the above methods have problems in that time taken to supply a dampening solution and printing ink at initial printing stage is not so short, and stain remains at non-image portions of prints printed at initial printing stage.